$re = '/\[\[ *fi(?:le|chier) *: *([^\|\]]*)[^\]]*\]\]/mi';
$str = '{{Infobox xyz
|aaa= Xyz
|bbb= [[Xyz]]
|ccc=[[File:xyz.jpg|thumb|Xyz.]]
|ddd= {{lang|en|xyz}}
}}
[[File:abc.jpg|thumb|Abc.]]';
$subst = "$1";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php